This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2001-242672 filed on Aug. 9, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a rotary pump, in particular, an internal gear pump such as a trochoid pump with higher discharge pressure and a brake apparatus having the same.
2. Description of Related Art
JP-A-2000-179466 shows a rotary pump, as an internal gear pump such as a trochoid pump or the like. The rotary pump is comprised of a drive shaft, an inner rotor having outer teeth portions and an outer rotor having inner teeth portions and a casing for containing the inner and outer rotors. The inner and outer rotors contained in the casing form a plurality of teeth gap portions surrounded by inner teeth portions of the outer rotor and outer teeth portions of the inner rotor which are in mesh with each other.
An intake port and a discharge port are separately disposed on opposite sides of a pump center line passing through the respective rotation axes of the inner and outer rotors. When the drive shaft is rotated for driving the pump, the inner rotor is rotated by the drive shaft on an axis of the drive shaft and, according to the rotation of the inner rotor, the outer rotor is rotated in the same direction. As the respective volumes of the teeth gap portions between the inner and outer teeth portions are varied every turn of the rotating inner and outer rotors, fluid is sucked from the intake port and discharged to the discharge port.
In the conventional rotary pump mentioned above, there is provided two side sealing members one of which seals an upper side clearance between the axial end surfaces of the rotors and the casing and the other of which seals a lower side clearance therebetween. Each of the side sealing members is composed of a resin member and an elastic member such as rubber which urges the resin member toward the outer and inner rotors.
It is not preferable from a cost standpoint to apply two pieces of the side sealing member, which are relatively expensive, to the rotary pump. Accordingly, it is contemplated that one of the upper and lower side clearances is sealed by the conventional resin side sealing member and the other of the upper and lower side clearances is sealed with mechanical sealing due to a direct contact between the axial end surfaces of the rotors and the casing.
For a purpose of assuring the mechanical sealing, it is necessary for the axial end surfaces of the rotors that are made of metal to be strongly pressed against the axial end surface of the casing that is also made of metal. If the contact frictional resistance is larger and, thus, torque loss is larger, a body of the rotary pump has to be larger to secure a given discharge output of the pump.
Further, if the sliding contact surface between the axial end surfaces of the rotors and the casing has a portion where the torque loss is relatively larger and another portion where the torque loss is not so large, frictional heat generated at the portion where the torque loss is large causes to expand metal material of the rotors and the casing, when the pump is rotated at high speed for a long time, so that the discharge output of the pump is damaged and deteriorated.
In the conventional rotary pump, the axial end surfaces of the outer and inner rotors and the axial end surface of a side plate, which are opposed to each other, are provided with parallel straight line gliding stripes formed by flat face grinding. If the axial end surfaces of outer and inner rotors and the side plate having the parallel straight line grinding stripes are in pressurized direct contact with each other for the mechanical sealing, there exist local portions of the sliding contact surface therebetween where the frictional resistance are larger and the torque loss are larger.
In a case as a typical example, as shown in FIG. 9, that an entire axial end surface of the side plate is provided with parallel straight line grinding stripes extending straight in parallel in a direction of connecting an intake port and a discharge port and entire axial end surfaces of the outer and inner rotors are also provided with parallel straight line grinding stripes, at a pair of arch shaped portions of the side plate positioned above a maximum volume closed teeth gap portion and below a minimum volume closed teeth gap portion in FIG. 9, lines of the parallel straight line grinding stripes extend straight in parallel without crossing the teeth gap portions formed by the outer and inner rotors in mech. Accordingly, fluid hardly flows from the teeth gap portions to these arch shaped portions through extremely slight gaps formed by slight concave and convex of the sliding stripes of the side plate.
On the other hand, there also exist a pair of arch shaped portions of the outer rotor where lines of the parallel straight line grinding stripes extend straight in parallel without crossing the teeth gap portions. Accordingly, when the lines of the parallel straight line grinding stripes of the side plate coincide with the lines of the parallel straight line grinding stripes according to the rotation of the rotors, that is, when the arch shaped portions of the side plate and the outer rotor are completely overlapped with each other, fluid lubrication is very poor at the arch shaped portions overlapped, since the extremely slight gaps formed by the sliding stripes of the side plate and the outer rotor do not communicate with the teeth gap portions. As the outer rotor rotate, the lines of the parallel straight line grinding stripes of the side plate and the outer rotor come to cross each other. However, the lines of the parallel straight line grinding stripes of the outer rotor that extend so as to cross the teeth gap portions gradually cross the lines of the parallel straight line grinding stripes on the arch shaped portion of the side plate. Therefore, fluid lubrication on the arch shaped portion of the side pate is inherently poor and the torque loss at the arch shaped portion is larger as shown in FIG. 9.
Torque loss is relatively small, as shown in FIG. 9, at contact surface portions of the side plate other than the arch shaped portions thereof, that is, at portions radially outside the teeth gap portions and perpendicular to a line of connecting the arch shaped portions, since the lines of the parallel straight line grinding stripes extend so as to always cross the teeth gap portions at these portions, irrelevant to the rotation angle of the outer rotor.
Further, if the axial end surfaces of the side plate and the outer rotor are provided with circumferential line grinding stripes, majority lines of the circumferential line grinding stripes at the contact surface between the side plate and the outer rotor do not extend to cross the teeth gap portions so that the fluid lubrication is very poor and the torque loss is larger on the contact surface therebetween.
The portions where the torque loss is larger are confirmed by extensive experimental tests of the present inventors from standpoints that larger torque results in larger heat generation and smaller torque in smaller heat generation, when the outer and inner rotors rotate, since, if the contact surfaces between the side plate and the outer and inner rotors are well lubricated by the fluid, the frictional resistance of the contact surfaces is smaller with less frictional heat and, if the contact surfaces are not well lubricated, the frictional resistance thereof is larger with more frictional heat.
An object of the present invention is to provide a rotary pump in which axial end surfaces of outer and inner rotors are in direct contact with an axial end surface of side plate (inner side surface of a casing) with less and/or uniform torque loss.
It is another object of the present invention to provide a brake apparatus having a hydraulic circuit in which the rotary pump mentioned above is disposed.
To achieve the object mentioned above, the rotary pump has an outer rotor provided at an inner circumference thereof with inner teeth, an inner rotor provided at an outer circumference thereof with outer teeth in mesh with the inner teeth so as to constitute a plurality of teeth gap portions including a first closed gap portion whose teeth gap volume is nearly largest and a second closed gap portion whose teeth gap volume is nearly smallest, a drive shaft fitted to the inner rotor for rotating the inner rotor, and a casing provided with intake and discharge ports and a rotor room in which the inner and outer rotors are rotatably contained in such a manner that first and second inner side surfaces of the rotor room face first and second axial end surfaces of the outer and inner rotors, respectively, with a circumference gap between an inner circumferential surface of the pump room and an outer circumferential surface of the outer rotor, and the intake and discharge ports communicate with the teeth gap portions so that fluid is sucked from the intake port and discharged from the discharge port when the drive shaft is driven. The rotary pump further has a side sealing member disposed between the first axial end surfaces of the outer and inner rotors and the first inner side surface of the pump room to urge the outer and inner rotors toward the second inner side surface of the pump room so that not only a side clearance between the first axial end surfaces of the outer and inner rotors and the first inner side surface of the pump room is sealed but also a side clearance between the second axial end surfaces of the outer and inner rotors and the second inner side surface of the pump room is sealed with a mechanical seal due to direct contact therebetween.
With the rotary pump mentioned above, both of the second axial end surfaces of the outer and inner rotors and the second inner side surface of the pump room are provided on entire surfaces thereof with radial line grinding stripes.
The radial line grinding stripes serves not only to lubricate the contact surface between the second axial end surfaces of the outer and inner rotors and the second inner side surface of the pump room through extremely slight gaps radially extending and always communicating with the teeth gap portions and the outer circumference gap but also to lubricate the contact surface through the extremely slight gaps with fluid receiving a centrifugal force acting radially according to the rotation of the outer and inner rotors. Accordingly, the frictional resistance and the torque loss at the contact surface are smaller.
As an alternative, in the rotary pump in which the second inner side surface of the pump room is provided with parallel straight line grinding stripes extending straight in parallel in a direction of connecting the intake port and the discharge port and the second axial end surfaces of the outer and inner rotors are also provided with parallel straight line grinding stripes, the second inner side surface of the pump room may be further provided in a vicinity of first and second closed gap portions with fluid grooves communicating with the outer circumference gap but not communicating with the teeth gap portions.
The fluid grooves serve to reduce an area of portions (arch shaped portions mentioned above) of the contact surface between the casing and the outer rotor where the frictional resistance is higher so that torque loss at these portions is reduced.
Further, as another alternative, the rotary pump may has an structure that one of the second axial end surfaces of the outer and inner rotors and the second inner side surface of the pump room is provided with radial line grinding stripes and the other thereof is provided with circumferential line grinding stripes.
In this case, contact frictional resistance at any portion of the contact surface between the outer and inner rotors and the pump room in any rotating phase is smaller, since there exist no arch shaped portions which the conventional rotary pump has and adequate size of extremely slight gaps are formed by the radial line and circumferential line grinding stripes whose lines always cross perpendicularly to each other, resulting in less frictional resistance and torque loss.
The radial line grinding stripes may be lines extending radially straight. In this case, the fuel can effectively flow along these lines due to the centrifugal force applied thereto.
The radial line grinding stripes may be lines extending radially in a curve. These curved lines can be easily formed when the outer and/or inner rotors or the pump room move relative to the grindstone whose curvature radius is relatively small.
Each line of the radial line grinding stripes of the pump room is curved in a direction opposite to each line of the radial line grinding stripes of the axial end surfaces of the outer and inner rotors.
One side of the radial line grinding stripes of the second axial end surfaces of the outer and inner rotors and the radial line grinding stripes of the second inner side surface of the pump room extend radially in straight and the other side thereof extend radially in a curve. The one side of the radial line grinding stripes may extend from a first center point radially outward in a curve and the other side thereof extend from a second center point, which is not coincident with the first center point, radially outward in a curve.
Furthermore, in the rotary pump in which the second axial end surface of the outer rotor and the second inner side surface of the pump room are provided on entire surfaces thereof with parallel straight line grinding stripes so that directions in which the parallel straight line grinding stripes of the second axial end surface of the outer rotor and the second inner side surface of the pump room coincide with each other in every half rotation of the outer rotor in the pump room, at least one of the second axial end surface of the outer rotor and the second inner side surface of the pump room may be provided at arch shaped positions, where each line of the parallel straight line grinding stripes penetrates in straight from a point of the outer circumference gap to another point thereof without crossing the teeth gap portions, with fluid grooves communicating with the outer circumference gap but not communicating with the teeth gap portions.
In this case, even if the arch shaped positions of the pump room are overlapped with the arch shaped position of the outer rotor according to the rotation of the outer rotor, an area of contact surface between the arch shaped positions of the pump room and the outer rotor is smaller due to the fluid grooves formed at one of the arch shaped positions thereof so that frictional resistance on these arch shaped positions is smaller, resulting in less torque loss. The arch shaped positions of the pump room in this case where the torque loss is higher are not limited to positions radially outside the first and second closed teeth gap portions, as shown in FIG. 9, but may be the other portions depending on line directions of the parallel straight grinding stripes on the pump room.
Moreover, in a rotary pump having an outer rotor provided at an inner circumference thereof with inner teeth, an inner rotor provided at an outer circumference thereof with outer teeth in mesh with the inner teeth so as to constitute a plurality of teeth gap portions, a drive shaft fitted to the inner rotor for rotating the inner rotor, a casing provided with intake and discharge ports and a rotor room in which the inner and outer rotors are rotatably contained with an outer circumference gap between an inner circumferential surface of the rotor room and an outer circumferential surface of the outer rotor in such a manner that at least one of opposite side axial end surfaces of the outer and inner rotors are in pressurized direct contact with toward one of opposite side inner side surfaces of the pump room to form a mechanical sealing and the intake port communicates with a first group of the teeth gap portions positioned between the second and first closed gap portions and the discharge port communicates with a second group of the teeth gap portions positioned between the first and second closed gap portions so that fluid is sucked from the intake port and discharged from the discharge port when the drive shaft is driven, and a circumference sealing member disposed in the outer circumference gap to divide the outer circumference gap into high and low pressure regions communicating with the intake and discharge ports, respectively, the one of the opposite side inner side surfaces of the pump room may be provided with a fluid groove communicating with the one of the high and low pressure regions but neither communicating with the other of the high and low pressure regions nor the teeth gap portions.
According to the rotary pump mentioned above, the fluid groove is provided, irrelevant to directions in which lines of the grinding stripes extend, to reduce an area of the contact surface between the pump room and the outer rotor so that the fluid groove serves to reduce the frictional resistance and the torque loss at the contact surface therebetween.
It is preferable, in this case, that the fluid groove is positioned radially outside the second group of the teeth gap portions communicating with the discharge port and radially inside the high pressure region of the outer circumference gap.
In a side clearance sealed by the mechanical sealing, fluid tends to flow from the high pressure region of the outer circumference gap or the second group of the teeth gap portion toward the first group of the teeth gap portions and the low pressure region of the outer circumference gap, due to pressure difference therebetween. However, the fluid hardly flows from the high pressure region of the outer circumference gap toward the second group of the teeth gap portion, because of on pressure difference therebetween, except the fluid movement along the lines of the grinding stripes or due to the centrifugal force acting radially. therefore, the fluid groove, which is formed at a position where the lubrication is very poor and the frictional resistance is higher, serves to reduce a contact surface between the pump room and the outer rotor and reduce the torque loss at this position.